Growth of Internet traffic, fueled by the growth in the number of users and by increasing numbers of applications, results in a higher demand for bandwidth. This growth entails larger packet networks with greater switching capabilities. Data centers contain huge numbers of racks of servers, racks of storage devices, and other racks, all of which are interconnected via a massive centralized packet switching resource. In data centers, electronic packet switches are used to route data packets. Electronic packet switching at very high rates involves massive cooling and space costs. Packets may be transmitted optically. Thus, photonic packet switching is desirable.
The racks of servers, storage, and input-output functions contain switches which combine packet streams from their associated servers and/or other peripherals into a smaller number of high speed streams per switch which are routed to the packet switching core. Due to the common location of these switches as the highest component in the switch, such a switch is often referred to as Top Of Rack (TOR) switch, or simply a TOR. It should be noted that TORs need not always be installed at the top of a rack. Also, TORs receive the returning switched streams from that resource and distribute them to servers within their rack. There may be 4×40 Gb/s streams from each TOR to the packet switching core, and the same number of return streams. There may be one TOR per rack, with hundreds to tens of thousands of racks, and hence hundreds to tens of thousands of TORs in a data center.